An X-ray computed tomography (CT) device computationally reconstructs a tomographic image (hereinafter, referred to as a CT image) of a subject by imaging X-ray transmission data of the subject while rotating an X-ray source and a pair of X-ray detectors (hereinafter, referred to as a scanner) which are disposed to face each other across the subject. The X-ray CT device is widely used in the field of industrial and security-purpose inspection devices or medical image diagnostic devices. In the field of a medical X-ray CT device, in recent years, the X-ray detector has occupied the larger area, and a scanner has been rotated faster. Accordingly, a wide imaging region can be measured in a short period of time. In addition, the faster rotation speed of the scanner improves time resolution. As a result, measurement accuracy is significantly improved for a moving subject such as the heart and coronary arteries. In accordance with the highly improved accuracy in X-ray CT measurement, there is a growing need for improved spatial resolution. For example, there is a need for following up whether or not a restenosis appears or a plaque status, through the inside of a stent inserted into a stenosed blood vessel in order to dilate the stenosed blood vessel. High spatial resolution is required in order to inspect a micro-structure of the subject.
In order to improve the spatial resolution for measurement using the X-ray CT device, a detection element of the X-ray detector normally needs to be miniaturized, that is, a size thereof needs to be reduced. However, in a case where X-ray doses incident on the X-ray detector are the same as each other, if the detection element is miniaturized, the number of X-ray photons incident on one detection element decreases. Accordingly, an signal-to-noise ratio of a detection signal is degraded. In order to improve the signal-to-noise ratio, it is necessary to increase the X-ray doses. However, in a case of medical measurement, an increase in the X-ray doses results in an increase in X-ray exposures of a subject to be tested. For the above-described reason, the size of the detection element of the X-ray detector is determined by the trade-off between the spatial resolution and the X-ray exposure amount. A medical X-ray CT device normally employs an X-ray element having an X-ray input surface whose size is approximately 1 mm square.
On the other hand, as a method of improving the spatial resolution (or decreasing artifacts) without reducing the size of the detection element of the X-ray detector, a method calling a flying focal spot (FFS) method has been proposed (refer to NPL 1). According to the FFS method, positions of X-ray focal points of adjacent views are shifted from each other so that an X-ray trajectory extending from an X-ray focal point to each X-ray detection element of the X-ray detector and an X-ray trajectory of the adjacent view are shifted in the X-ray detector coordinate system. According to NPL 1, this configuration improves the resolution mainly at a rotation center.
PTL 1 discloses a configuration in which the positions of the X-ray focal points are shifted so that the positions of the X-ray focal points are the same as each other in the adjacent views. In this manner, each of the X-ray trajectories of a certain view exactly pass (interlaces) through gaps of the X-ray trajectories of the adjacent view. In this manner, a relationship is established so that the X-ray trajectories of the adjacent views completely interlace with each other not only at the rotation center but also in all imaging regions. Therefore, the resolution is also improved in the region in addition to the rotation center.